diff --git a/include/ksr/promises.h b/include/ksr/promises.h
index 2211fca..7eaf794 100644
--- a/include/ksr/promises.h
+++ b/include/ksr/promises.h
@@ -14,6 +14,7 @@ typedef struct {
 	pthread_t thread;
 	ksrarray *then_callbacks; // array of then callbacks.
 	ksrarray *catch_callbacks; // array of catch callbacks.
+	ksrarray *finally_callbacks; // array of finally callbacks.
 
 	bool successful; // determine if the promise has been fulfilled or not.
 	void *result; // the promised result.
@@ -28,6 +29,8 @@ typedef void (*ksrpromise_execution_f)(ksrpromise *promise, void *userdata);
 typedef void (*ksrpromise_then_callback_f)(void *result, void *userdata);
 // type of catch callback.
 typedef void (*ksrpromise_catch_callback_f)(int code, const char *message, void *userdata);
+// type of finally callback.
+typedef void (*ksrpromise_finally_callback_f)(void *userdata);
 
 /**
  * Create a new promise.
@@ -63,6 +66,7 @@ void* ksrpromise_await(ksrpromise *promise);
  * Set a new callback to call on promise resolution.
  * @param promise - the promise for which to set a resolution callback.
  * @param callback - the callback to set.
+ * @param userdata - custom data to passed to the callback.
  */
 void ksrpromise_then(ksrpromise *promise, ksrpromise_then_callback_f, void *userdata);
 
@@ -70,9 +74,18 @@ void ksrpromise_then(ksrpromise *promise, ksrpromise_then_callback_f, void *user
  * Set a new callback to call on promise rejection.
  * @param promise - the promise for which to set a rejection callback.
  * @param callback - a callback to set.
+ * @param userdata - custom data to passed to the callback.
  */
 void ksrpromise_catch(ksrpromise *promise, ksrpromise_catch_callback_f, void *userdata);
 
+/**
+ * Set a new callback to call on promise resolution or rejection.
+ * @param promise - the promise for which to set a finally callback.
+ * @param callback - a callback to set.
+ * @param userdata - custom data to passed to the callback.
+ */
+void ksrpromise_finally(ksrpromise *promise, ksrpromise_finally_callback_f, void *userdata);
+
 /**
  * Determine if the given promise is successful or not.
  * @param - the promise to check.
diff --git a/src/promises.c b/src/promises.c
index 7a84bf0..b733863 100644
--- a/src/promises.c
+++ b/src/promises.c
@@ -40,6 +40,13 @@ typedef struct {
 	ksrpromise_catch_callback_f callback;
 	void *userdata;
 } promise_catch_user_callback;
+/**
+ * Promise finally user callback.
+ */
+typedef struct {
+	ksrpromise_finally_callback_f callback;
+	void *userdata;
+} promise_finally_user_callback;
 
 /**
  * The main promise thread function.
@@ -62,6 +69,7 @@ ksrpromise* ksrpromise_new(ksrpromise_execution_f exec, void *data)
 	ksrpromise *promise = malloc(sizeof(ksrpromise));
 	promise->then_callbacks = ksrarray_new_tiny();
 	promise->catch_callbacks = ksrarray_new_tiny();
+	promise->finally_callbacks = ksrarray_new_tiny();
 	promise->successful = false;
 	promise->result = NULL;
 	promise->error_code = 0;
@@ -166,3 +174,14 @@ void ksrpromise_catch(ksrpromise *promise, ksrpromise_catch_callback_f callback,
 	// we use a pointer of the given function pointer as a workaround for generic arrays (see https://stackoverflow.com/a/16682718/7496951).
 	ksrarray_push(promise->catch_callbacks, user_callback);
 }
+
+void ksrpromise_finally(ksrpromise *promise, ksrpromise_finally_callback_f callback, void *userdata)
+{
+	// allocate user callback.
+	promise_finally_user_callback *user_callback = malloc(sizeof(promise_finally_user_callback));
+	user_callback->callback = callback;
+	user_callback->userdata = userdata;
+
+	// we use a pointer of the given function pointer as a workaround for generic arrays (see https://stackoverflow.com/a/16682718/7496951).
+	ksrarray_push(promise->finally_callbacks, user_callback);
+}
diff --git a/tests/ksrpromises.c b/tests/ksrpromises.c
index 73e0289..8576d8c 100644
--- a/tests/ksrpromises.c
+++ b/tests/ksrpromises.c
@@ -44,12 +44,20 @@ void on_promise_failed(int error_code, const char *error_message, void *userdata
 	assert(str_equals("blabla", userdata));
 }
 
+void on_promise_finished(void *userdata)
+{
+	// checking that user data have been properly transfered.
+	assert(str_equals("test_finally", userdata));
+}
+
 int main(void)
 {
 	// try to create a promise.
 	ksrpromise *promise = ksrpromise_new(promise_execution_ok, NULL);
 	// checking that then is properly launched.
 	ksrpromise_then(promise, on_promise_ok, NULL);
+	// checking that finally is properly launched.
+	ksrpromise_finally(promise, on_promise_finished, "test_finally");
 	// checking that await is working properly on a successful promise.
 	assert(str_equals("OK", ksrpromise_await(promise)));
 
@@ -57,6 +65,8 @@ int main(void)
 	ksrpromise *promise_fail = ksrpromise_new(promise_execution_error, "hello");
 	// checking that catch is properly launched.
 	ksrpromise_catch(promise_fail, on_promise_failed, "blabla");
+	// checking that finally is properly launched.
+	ksrpromise_finally(promise, on_promise_finished, "test_finally");
 	// checking that await is working properly on a promise which fails.
 	assert(ksrpromise_await(promise_fail) == NULL);